22 week assessment of bladder acellular matrix as a bladder augmentation material in a porcine model

Active and passive material response of urinary bladder smooth muscle tissue in uniaxial and biaxial tensile testing

The urinary bladder is a hollow organ that undergoes significant deformation as it receives, stores, and releases urine. To understand the organ mechanics, it is necessary to obtain information about the material properties of the tissues involved. In displacement-controlled tensile tests, tissue samples are mounted on a device that applies stretches to the tissue in one or more directions, resulting in a specific stress response. For this study, we performed uniaxial and biaxial stretch experiments on tissue samples (n = 36) from the body region of the porcine urinary bladder. We analyzed the stress-relaxation, activation dynamics, and passive and active stretch-stress response. Main findings of our experiments are: (1) For uniaxial and biaxial stretching, the time constants for stress-relaxation depend on the stretch amplitude, (2) biaxially stretched samples experienced slower activation with τact increasing by +63% compared to uniaxial stretching, (3) biaxial tests are characterized by reduced optimum stretches λopt by -18%, and (4) biaxial and uniaxial tests showed no significant difference in maximum active stresses σopt. To interpret the results, we present a continuum mechanical model based on a viscoelastic, isotropic solid extended by a set of active muscle fibers. Model predictions show that results (3) and (4) can be explained by a uniform distribution of fiber orientations and a specific shape of the active fiber stress-stretch relationship. This study highlights how deformation modes during tensile testing affects smooth muscle mechanics, proving insights for interpreting experimental data and improving organ modeling. STATEMENT OF SIGNIFICANCE: In this study, we examined the mechanical properties of porcine bladder smooth muscle using uniaxial and equibiaxial tensile tests. To our knowledge, this is the first instance where the active stress-stretch relationships of smooth muscle tissue have been analysed under equibiaxial stretch. The data collected offer a detailed understanding of the connection between deformation and active stress production, surpassing the insights provided by existing uniaxial tests in the literature. These findings are crucial for comprehending the physiology of smooth muscle tissue and for developing constitutive muscle models that can make more accurate predictions about the functionality of hollow organs in both health and disease. Additionally, our findings on smooth muscle active stress could aid in the creation of biomaterials that interact with or even replace natural muscle.

Bladder Reconstruction in Cats Using In-Body Tissue Architecture (iBTA)-Induced Biosheet

Urinary tract diseases are common in cats, and often require surgical reconstruction. Here, to explore the possibility of urinary tract reconstruction in cats using in-body tissue architecture (iBTA), biosheets fabricated using iBTA technology were implanted into the feline bladder and the regeneration process was histologically evaluated. The biosheets were prepared by embedding molds into the dorsal subcutaneous pouches of six cats for 2 months. A section of the bladder wall was removed, and the biosheets were sutured to the excision site. After 1 and 3 months of implantation, the biosheets were harvested and evaluated histologically. Implantable biosheets were formed with a success rate of 67%. There were no major complications following implantation, including tissue rejection, severe inflammation, or infection. Urinary incontinence was also not observed. Histological evaluation revealed the bladder lumen was almost entirely covered by urothelium after 1 month, with myofibroblast infiltration into the biosheets. After 3 months, the urothelium became multilayered, and mature myocytes and nerve fibers were observed at the implantation site. In conclusion, this study showed that tissue reconstruction using iBTA can be applied to cats, and that biosheets have the potential to be useful in both the structural and functional regeneration of the feline urinary tract.

Active viscoelastic models for cell and tissue mechanics

Living cells are out of equilibrium active materials. Cell-generated forces are transmitted across the cytoskeleton network and to the extracellular environment. These active force interactions shape cellular mechanical behaviour, trigger mechano-sensing, regulate cell adaptation to the microenvironment and can affect disease outcomes. In recent years, the mechanobiology community has witnessed the emergence of many experimental and theoretical approaches to study cells as mechanically active materials. In this review, we highlight recent advancements in incorporating active characteristics of cellular behaviour at different length scales into classic viscoelastic models by either adding an active tension-generating element or adjusting the resting length of an elastic element in the model. Summarizing the two groups of approaches, we will review the formulation and application of these models to understand cellular adaptation mechanisms in response to various types of mechanical stimuli, such as the effect of extracellular matrix properties and external loadings or deformations.

Multipotent bone marrow cell-seeded polymeric composites drive long-term, definitive urinary bladder tissue regeneration

To date, there are no efficacious translational solutions for end-stage urinary bladder dysfunction. Current surgical strategies, including urinary diversion and bladder augmentation enterocystoplasty (BAE), utilize autologous intestinal segments (e.g. ileum) to increase bladder capacity to protect renal function. Considered the standard of care, BAE is fraught with numerous short- and long-term clinical complications. Previous clinical trials employing tissue engineering approaches for bladder tissue regeneration have also been unable to translate bench-top findings into clinical practice. Major obstacles still persist that need to be overcome in order to advance tissue-engineered products into the clinical arena. These include scaffold/bladder incongruencies, the acquisition and utility of appropriate cells for anatomic and physiologic tissue recapitulation, and the choice of an appropriate animal model for testing. In this study, we demonstrate that the elastomeric, bladder biomechanocompatible poly(1,8-octamethylene-citrate-co-octanol) (PRS; synthetic) scaffold coseeded with autologous bone marrow-derived mesenchymal stem cells and CD34+ hematopoietic stem/progenitor cells support robust long-term, functional bladder tissue regeneration within the context of a clinically relevant baboon bladder augmentation model simulating bladder trauma. Partially cystectomized baboons were independently augmented with either autologous ileum or stem-cell-seeded small-intestinal submucosa (SIS; a commercially available biological scaffold) or PRS grafts. Stem-cell synergism promoted functional trilayer bladder tissue regeneration, including whole-graft neurovascularization, in both cell-seeded grafts. However, PRS-augmented animals demonstrated fewer clinical complications and more advantageous tissue characterization metrics compared to ileum and SIS-augmented animals. Two-year study data demonstrate that PRS/stem-cell-seeded grafts drive bladder tissue regeneration and are a suitable alternative to BAE.

Perfusion preparation of the rat bladder decellularized scaffold

Introduction

Bladder reconstruction is a huge challenge in the field of urology. In recent years, perfusion methods have brought promising results in the field of tissue engineering. We prepared bladder decellularized scaffolds by improved perfusion, which may be suitable for bladder reconstruction.

Methods

We prepared decellularized scaffolds of rat bladder by perfusion of SDS (0.5% sodium dodecyl sulfate), SDS-SDC (0.5% sodium dodecyl sulfate +0.5% sodium deoxycholate). Histological characteristics of bladder decellularized scaffolds were assessed by Hematoxylin and eosin, Masson, and DAPI staining. Moreover, we also prepared a murine bladder transplantation model to evaluate the regenerative potential of scaffolds.

Results

Hematoxylin and eosin, Masson, and DAPI staining indicated almost no cellular component residues in the SDS-SDC group. Histological analysis (hematoxylin and eosin staining, Masson staining), CD31 and F4/80 staining analysis, one month after implantation, revealed that the decellularized scaffolds had regenerative characteristics, and the SDS-SDC scaffold had better regenerative properties than the SDS scaffold.

Conclusions

We successfully prepared the decellularized scaffold for the rat bladder by perfusion. Our results showed that the SDS-SDC scaffold had better decellularization efficiency and reconstruction ability than the SDS scaffold, which provides a new perspective on bladder reconstruction materials.

Augmentation cystoplasty in dogs: A comparative study of different tunica vaginalis grafts

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Tunica vaginalis allograft and sheep tunica vaginalis decellularized extracellular matrix successfully rebuilt the bladder wall with minor complications in dogs.

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Sheep tunica vaginalis xenograft has disappointing results in the canine model since the bladders became contracted with decreased capacity.

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Tunica vaginalis grafts represent a simple and low-cost choice for augmentation cystoplasty in dogs.

In veterinary practice, numerous urological disorders that cause bladder dysfunction necessitate augmentation cystoplasty (AC). The purpose of this study is to evaluate the dog tunica vaginalis allograft (DTVA), sheep tunica vaginalis xenograft (STVX) and sheep tunica vaginalis decellularized extracellular matrix (STVDEM) as graft materials for urinary bladder (UB) reconstruction following a 45±5% cystectomy model in dogs. In this study, 18 adult apparently healthy mongrel dogs of both sexes were divided into three groups (6 dogs each): the DTVA group, the STVX group, and the STVDEM group. The evaluation of the AC in different groups was carried out using clinical, hematological, serum biochemical, urine, ultrasonographic, retrograde positive cystogram, and histopathological analysis all over the study period of 12 weeks. The dogs in all groups survived the procedures, except three dogs died from both STVX and DTVA groups. The mean bladder capacity indicated that the DTVA and STVX groups had regained 82.22% and 68.62%, respectively, of their preoperative baseline capacity. Interestingly, the STVDEM group's bladder capacity increased to 113.70%. Although histological analysis revealed that the three grafts successfully rebuilt the bladder wall, the STVDEM demonstrated well-organized and well-differentiated epithelial and muscular tissues that resembled, but were not identical to, native UB tissues. As a result, STVDEM is proposed as an ideal and potential acellular graft for UB reconstruction in dogs, whereas DTVA and STVX could be employed in emergencies requiring UB reconstruction.

Association mapping uncovers maize ZmbZIP107 regulating root system architecture and lead absorption under lead stress

Lead (Pb) is a highly toxic contaminant to living organisms and the environment. Excessive Pb in soils affects crop yield and quality, thus threatening human health via the food chain. Herein, we investigated Pb tolerance among a maize association panel using root bushiness (BSH) under Pb treatment as an indicator. Through a genome-wide association study of relative BSH, we identified four single nucleotide polymorphisms (SNPs) and 30 candidate genes associated with Pb tolerance in maize seedlings. Transcriptome analysis showed that four of the 30 genes were differentially responsive to Pb treatment between two maize lines with contrasting Pb tolerance. Among these, the ZmbZIP107 transcription factor was confirmed as the key gene controlling maize tolerance to Pb by using gene-based association studies. Two 5' UTR_variants in ZmbZIP107 affected its expression level and Pb tolerance among different maize lines. ZmbZIP107 protein was specifically targeted to the nucleus and ZmbZIP107 mRNA showed the highest expression in maize seedling roots among different tissues. Heterologous expression of ZmbZIP107 enhanced rice tolerance to Pb stress and decreased Pb absorption in the roots. Our study provided the basis for revelation of the molecular mechanism underlying Pb tolerance and contributed to cultivation of Pb-tolerant varieties in maize.

Translation of mechanical strain to a scalable biomanufacturing process for acellular matrix production from full thickness porcine bladders

Bladder acellular matrix has promising applications in urological and other reconstructive surgery as it represents a naturally compliant, non-immunogenic and highly tissue-integrative material. As the bladder fills and distends, the loosely-coiled bundles of collagen fibres in the wall become extended and orientate parallel to the lumen, resulting in a physical thinning of the muscular wall. This accommodating property can be exploited to achieve complete decellularisation of the full-thickness bladder wall by immersing the distended bladder through a series of hypotonic buffers, detergents and nucleases, but the process is empirical, idiosyncratic and does not lend itself to manufacturing scale up. In this study we have taken a mechanical engineering approach to determine the relationship between porcine bladder size and capacity, to define the biaxial deformation state of the tissue during decellularisation and to apply these principles to the design and testing of a scalable novel laser-printed flat-bed apparatus in order to achieve reproducible and full-thickness bladder tissue decellularisation. We demonstrate how the procedure can be applied reproducibly to fresh, frozen or twice-frozen bladders to render8×8 cm²patches of DNA-free acellular matrix suitable for surgical applications.

Tissue engineering to treat pelvic organ prolapse

Pelvic organ prolapse (POP) is a frequent chronic illness, which seriously affects women's living quality. In recent years, tissue engineering has made superior progress in POP treatment, and biological scaffolds have received considerable attention. Nevertheless, pelvic floor reconstruction still faces severe challenges, including the construction of ideal scaffolds, the selection of optimal seed cells, and growth factors. This paper summarizes the recent progress of pelvic floor reconstruction in tissue engineering, and discusses the problems that need to be further considered and solved to provide references for the further development of this field.

Urinary bladder augmentation with acellular biologic scaffold-A preclinical study in a large animal model

Current strategies in urinary bladder augmentation include use of gastrointestinal segments, however, the technique is associated with inevitable complications. An acellular biologic scaffold seems to be a promising option for urinary bladder augmentation. The aim of this study was to evaluate the utility of bladder acellular matrix (BAM) for reconstruction of clinically significant large urinary bladder wall defects in a long-term porcine model. Urinary bladders were harvested from 10 pig donors. Biological scaffolds were prepared by chemically removing all cellular components from urinary bladder tissue. A total of 10 female pigs underwent hemicystectomy and subsequent bladder reconstruction with BAM. The follow-up study was 6 months. Reconstructed bladders were subjected to radiological, macroscopic, histological, immunohistochemical, and molecular evaluations. Six out of ten animals survived the 6-month follow-up period. Four pigs died during observation due to mechanical failure of the scaffold, anastomotic dehiscence between the scaffold and native bladder tissue, or occluded catheter. Tissue engineered bladder function was normal without any signs of postvoid residual urine in the bladder or upper urinary tracts. Macroscopically, graft shrinkage was observed. Urothelium completely covered the luminal surface of the graft. Smooth muscle regeneration was observed mainly in the peripheral graft region and gradually decreased toward the center of the graft. Expression of urothelial, smooth muscle, blood vessel, and nerve markers were lower in the reconstructed bladder wall compared to the native bladder. BAM seems to be a promising biomaterial for reconstruction of large urinary bladder wall defects. Further research on cell-seeded BAM to enhance urinary bladder regeneration is required.

Regeneration of muscular wall of the bladder using a ureter matrix graft as a scaffold

We investigated a method for bladder augmentation in rats using a decellularized ureter graft. We used 16 rats divided into two groups of eight. After partial cystectomy, the bladders in group 1 were grafted with a 1 cm² patch of human decellularized ureter. Rats in group 2 were untreated controls. Biopsies of the graft were taken at 1, 3 and 9 months postoperatively for histological investigation. Total removal of cells and preservation of extracellular matrix (ECM) was confirmed in the decellularized ureter. Histological examination after 1 month revealed few cells at the border of the graft. Three months after the operation, the graft was infiltrated by vessels and smooth muscle and the mucosal lining was complete. All bladder wall components resembled native bladder wall by 9 months after implantation. CD34, CD31, α-smooth muscle actin, S100, cytokeratin AE1/AE3 and vimentin were detected 9 months after the operation. We demonstrated the potential of decellularized biocompatible ureteric grafts for use as a natural collagen scaffold for bladder repair in rats.

Sterilization and disinfection methods for decellularized matrix materials: Review, consideration and proposal

Sterilization is the process of killing all microorganisms, while disinfection is the process of killing or removing all kinds of pathogenic microorganisms except bacterial spores. Biomaterials involved in cell experiments, animal experiments, and clinical applications need to be in the aseptic state, but their physical and chemical properties as well as biological activities can be affected by sterilization or disinfection. Decellularized matrix (dECM) is the low immunogenicity material obtained by removing cells from tissues, which retains many inherent components in tissues such as proteins and proteoglycans. But there are few studies concerning the effects of sterilization or disinfection on dECM, and the systematic introduction of sterilization or disinfection for dECM is even less. Therefore, this review systematically introduces and analyzes the mechanism, advantages, disadvantages, and applications of various sterilization and disinfection methods, discusses the factors influencing the selection of sterilization and disinfection methods, summarizes the sterilization and disinfection methods for various common dECM, and finally proposes a graphical route for selecting an appropriate sterilization or disinfection method for dECM and a technical route for validating the selected method, so as to provide the reference and basis for choosing more appropriate sterilization or disinfection methods of various dECM.

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Asepsis is the prerequisite for the experiment and application of biomaterials.

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Sterilization or disinfection affects physic-chemical properties of biomaterials.

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Mechanism, advantages and disadvantages of sterilization or disinfection methods.

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Factors influencing the selection of sterilization or disinfection methods.

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Selection of sterilization or disinfection methods for decellularized matrix.

Location- and layer-dependent biomechanical and microstructural characterisation of the porcine urinary bladder wall

The knowledge of the mechanical properties of the urinary bladder wall helps to explain its storage and micturition functions in health and disease studies; however, these properties largely remain unknown, especially with regard to its layer-specific characteristics and microstructure. Consequently, this study entails the assessment of the layer-specific differences in the mechanical properties and microstructure of the bladder wall, especially during loading. Accordingly, ninety-two (n=92) samples of porcine urinary bladder walls were mechanically and histologically analysed. Generally, the bladder wall and different tissue layers exhibit a non-linear stress-stretch relationship. In this study, the load transfer mechanisms were not only associated with the wavy structure of muscular and mucosal layers, but also with the entire bladder wall microstructure. Contextually, an interplay between the mucosal and muscular layers could be identified. Therefore, depending on the region and direction, the mucosal layer exhibited a stiffer mechanical response to equi-biaxial loading than that offered by the muscular layer when deformed to stretch levels higher than λ=1.6 to λ=2.2. For smaller stretches, the mucosal layer evinces no significant mechanical reaction, while the muscular layer bears the load. Owing to the orientation of its muscle fibres, the muscular layer shows an increased degree of anisotropy compared to the mucosal layer. Furthermore, the general incompressibility assumption is analysed for different layers by measuring the change in thickness during loading, which indicated a small volume loss.

Urinary bladder reconstruction using autologous collagenous connective tissue membrane "Biosheet®" induced by in-body tissue architecture: A pilot study

INTRODUCTION

In-body tissue architecture (iBTA) technology, based on cell-free tissue engineering, can produces collagenous tissues for implantation by subcutaneous embedding a designed mold. The aim of this study was to evaluate the biocompatibility of iBTA-induced "Biosheet®" collagenous sheets, as scaffold materials for bladder reconstruction.

METHODS

Canine Biosheet® implants were prepared by embedding molds into subcutaneous pouches in beagles for 8 weeks. A part of canine bladder wall was excised (2 × 2 cm) and repaired by patching the same sized autologous Biosheet®. The Biosheet® implants were harvested 4 weeks (n = 1) and 12 weeks (n = 3) after the implantation and evaluated histologically.

RESULTS

No disruption of the patched Biosheet® implants or urinary leakage into the peritoneal cavity was observed during the entire observation periods. There were no signs of chronic inflammation or Biosheet® rejection. The urine-contacting surface of luminal surface of the Biosheet® was covered with a multicellular layer of urothelium cells 4 weeks after implantation. α-SMA-positive muscle cells were observed at the margin of the Biosheet® implants at 12 weeks after the implantation. In addition, in the center of the Biosheet® implants, the formation of microvessels stained as α-SMA-positive was observed.

CONCLUSION

Biosheet® implants have biocompatibility as a scaffold for bladder reconstruction, indicating that they may be applicable for full-thickness bladder wall substitution. Further studies are required for definitive evaluation as a scaffold for bladder reconstruction.

MRI method for labeling and imaging decellularized extracellular matrix scaffolds for tissue engineering

PURPOSE

To develop a facile method for labeling and imaging decellularized extracellular matrix (dECM) scaffolds intended for regenerating 3D tissues.

METHODS

A small molecule manganese porphyrin, MnPNH₂ , was synthesized and used to label dECM scaffolds made from porcine bladder and trachea and murine whole lungs. The labeling protocol was optimized on bladder dECM, and imaging on a 3T clinical scanner was performed to assess reductions in T₁ and T₂ relaxation times. In vivo MRI was performed on dECM injected in the rat dorsum to verify sensitivity of detection. Toxicity assays for cell viability, metabolism, and proliferation were performed on human umbilical vein endothelial cells. The incorporation of MnPNH₂ and its long-term retention in dECM were assessed on transmission electron microscopy and ultraviolet absorbance of eluted MnPNH₂ over time.

RESULTS

All tissues, including thick whole 3D organs, were uniformly labeled and demonstrated high signal-to-noise on MRI. A nearly 10-fold reduction in T₁ was consistently obtained at a labeling dose of 0.4 mM, and even 0.2 mM provided sufficient contrast in vivo and ex vivo. No toxicity was observed up to 0.4 mM, the maximum tested. Binding studies suggested nonspecific association, and retention studies in the labeled whole decellularized lungs revealed less than 20% MnPNH₂ loss over 30 days, the majority occurring in the first 3 days after labeling.

CONCLUSION

The proposed labeling method is the first report for visualizing dECM on MRI and has the potential for long-term monitoring and optimization of dECM-based organ tissue engineering.

Stem Cells Seeded on Multilayered Scaffolds Implanted into an Injured Bladder Rat Model Improves Bladder Function

Background

To investigate whether human adipose-derived stem cells (hADSCs) seeded on multilayered poly (l-lactide-co-ɛ-caprolactone) (PLCL) sheets improve bladder function in a rat model of detrusor smooth muscle-removed bladder.

Methods

Male rats were randomly divided into 4 groups: Normal, injury (detrusor smooth muscle-removed bladder), PLCL (detrusor smooth muscle-removed bladder implanted with PLCL sheets), and PLCL + ADSC (detrusor smooth muscle-removed bladder implanted with PLCL sheets seeded with hADSCs). Four weeks after the treatment, physiological, histological, immunohistochemical, and immunoblot analyses were performed.

Results

hADSCs were compatible with PLCL sheets. Further, the physiological study of PLCL + ADSC group showed significant improvement in compliance and contractility suggesting the functional improvement of the bladder. Histological, immunohistochemical and immunoblot analyses revealed the uniform distribution of hADSCs in between PLCL sheets as well as differentiation of hADSCs into smooth muscle cells (SMC) which is illustrated by the expression of SMC markers.

Conclusion

hADSCs seeded on the multilayered PLCL sheets has the potential to differentiate into SMC, thus facilitating the recovery of compliance and contractility of the injured bladder.

Tissue Engineering in Pediatric Bladder Reconstruction-The Road to Success

Several congenital disorders can cause end stage bladder disease and possibly renal damage in children. The current gold standard therapy is enterocystoplasty, a bladder augmentation using an intestinal segment. However, the use of bowel tissue is associated with numerous complications such as metabolic disturbance, stone formation, urine leakage, chronic infections, and malignancy. Urinary diversions using engineered bladder tissue would obviate the need for bowel for bladder reconstruction. Despite impressive progress in the field of bladder tissue engineering over the past decades, the successful transfer of the approach into clinical routine still represents a major challenge. In this review, we discuss major achievements and challenges in bladder tissue regeneration with a focus on different strategies to overcome the obstacles and to meet the need for living functional tissue replacements with a good growth potential and a long life span matching the pediatric population.

Elastic materials for tissue engineering applications: Natural, synthetic, and hybrid polymers

Elastin and collagen are the two main components of elastic tissues and provide the tissue with elasticity and mechanical strength, respectively. Whereas collagen is adequately produced in vitro, production of elastin in tissue-engineered constructs is often inadequate when engineering elastic tissues. Therefore, elasticity has to be artificially introduced into tissue-engineered scaffolds. The elasticity of scaffold materials can be attributed to either natural sources, when native elastin or recombinant techniques are used to provide natural polymers, or synthetic sources, when polymers are synthesized. While synthetic elastomers often lack the biocompatibility needed for tissue engineering applications, the production of natural materials in adequate amounts or with proper mechanical strength remains a challenge. However, combining natural and synthetic materials to create hybrid components could overcome these issues. This review explains the synthesis, mechanical properties, and structure of native elastin as well as the theories on how this extracellular matrix component provides elasticity in vivo. Furthermore, current methods, ranging from proteins and synthetic polymers to hybrid structures that are being investigated for providing elasticity to tissue engineering constructs, are comprehensively discussed.

STATEMENT OF SIGNIFICANCE

Tissue engineered scaffolds are being developed as treatment options for malfunctioning tissues throughout the body. It is essential that the scaffold is a close mimic of the native tissue with regards to both mechanical and biological functionalities. Therefore, the production of elastic scaffolds is of key importance to fabricate tissue engineered scaffolds of the elastic tissues such as heart valves and blood vessels. Combining naturally derived and synthetic materials to reach this goal proves to be an interesting area where a highly tunable material that unites mechanical and biological functionalities can be obtained.

Location-dependent correlation between tissue structure and the mechanical behaviour of the urinary bladder

The mechanical properties of the urinary bladder wall are important to understand its filling-voiding cycle in health and disease. However, much remains unknown about its mechanical properties, especially regarding regional heterogeneities and wall microstructure. The present study aimed to assess the regional differences in the mechanical properties and microstructure of the urinary bladder wall. Ninety (n=90) samples of porcine urinary bladder wall (ten samples from nine different locations) were mechanically and histologically analysed. Half of the samples (n=45) were equibiaxially tested within physiological conditions, and the other half, matching the sample location of the mechanical tests, was frozen, cryosectioned, and stained with Picro-Sirius red to differentiate smooth muscle cells, extracellular matrix, and fat. The bladder wall shows a non-linear stress-stretch relationship with hysteresis and softening effects. Regional differences were found in the mechanical response and in the microstructure. The trigone region presents higher peak stresses and thinner muscularis layer compared to the rest of the bladder. Furthermore, the ventral side of the bladder presents anisotropic characteristics, whereas the dorsal side features perfect isotropic behaviour. This response matches the smooth muscle fibre bundle orientation within the tunica muscularis. This layer, comprising approximately 78% of the wall thickness, is composed of two fibre bundle arrangements that are cross-oriented, one with respect to the other, varying the angle between them across the organ. That is, the ventral side presents a 60°/120° cross-orientation structure, while the muscle bundles were oriented perpendicular in the dorsal side.

STATEMENT OF SIGNIFICANCE

In the present study, we demonstrate that the mechanical properties and the microstructure of the urinary bladder wall are heterogeneous across the organ. The mechanical properties and the microstructure of the urinary bladder wall within nine specific locations matching explicitly the mechanical and structural variations have been examined. On the one hand, the results of this study contribute to the understanding of bladder mechanics and thus to their functional understanding of bladder filling and voiding. On the other hand, they are relevant to the fields of constitutive formulation of bladder tissue, whole bladder mechanics, and bladder-derived scaffolds i.e., tissue-engineering grafts.

Bladder regeneration in a canine model using a bladder acellular matrix loaded with a collagen-binding bFGF

Bladder reconstruction remains challenging for urological surgery due to lack of suitable regenerative scaffolds. In a previous study, we had used a collagen-binding basic fibroblast growth factor (CBD-bFGF) to bind bFGF to the collagen scaffold, which could promote bladder regeneration in rats. However, the limited graft size in rodent models cannot provide enough evidence to demonstrate the repair capabilities of this method for severely damaged bladders in humans or large animals. In this study, the CBD-bFGF was used to activate a bladder acellular matrix (BAM) scaffold, and the CBD-bFGF/BAM functional scaffold was assessed in a canine model with a large segment defect (half of the entire bladder was resected). The results demonstrated that the functional biomaterials could promote bladder smooth muscle, vascular, and nerve regeneration and improve the function of neobladders. Thus, the CBD-bFGF/BAM functional scaffold may be a promising biomaterial for bladder reconstruction.

Bioengineering Approaches for Bladder Regeneration

Current clinical strategies for bladder reconstruction or substitution are associated to serious problems. Therefore, new alternative approaches are becoming more and more necessary. The purpose of this work is to review the state of the art of the current bioengineering advances and obstacles reported in bladder regeneration. Tissue bladder engineering requires an ideal engineered bladder scaffold composed of a biocompatible material suitable to sustain the mechanical forces necessary for bladder filling and emptying. In addition, an engineered bladder needs to reconstruct a compliant muscular wall and a highly specialized urothelium, well-orchestrated under control of autonomic and sensory innervations. Bioreactors play a very important role allowing cell growth and specialization into a tissue-engineered vascular construct within a physiological environment. Bioprinting technology is rapidly progressing, achieving the generation of custom-made structural supports using an increasing number of different polymers as ink with a high capacity of reproducibility. Although many promising results have been achieved, few of them have been tested with clinical success. This lack of satisfactory applications is a good reason to discourage researchers in this field and explains, somehow, the limited high-impact scientific production in this area during the last decade, emphasizing that still much more progress is required before bioengineered bladders become a commonplace in the clinical setting.

Incorporation of nanoparticles into transplantable decellularized matrices: Applications and challenges

Decellularization of tissues can significantly improve regenerative medicine and tissue engineering by producing natural, less immunogenic, three-dimensional, acellular matrices with high biological activity for transplantation. Decellularized matrices retain specific critical components of native tissues such as stem cell niche, various growth factors, and the ability to regenerate in vivo. However, recellularization and functionalization of these matrices remain limited, highlighting the need to improve the characteristics of decellularized matrices. Incorporating nanoparticles into decellularized tissues can overcome these limitations because nanoparticles possess unique properties such as multifunctionality and can modify the surface of decellularized matrices with additional growth factors, which can be loaded onto the nanoparticles. Therefore, in this minireview, we highlight the various approaches used to improve decellularized matrices with incorporation of nanoparticles and the challenges present in these applications.

Tissue engineering in pediatric urology - a critical appraisal

Tissue engineering is defined as the combination of biomaterials and bioengineering principles together with cell transplantation or directed growth of host cells to develop a biological replacement tissue or organ that can be a substitute for normal tissue both in structure and function. Despite early promising preclinical studies, clinical translation of tissue engineering in pediatric urology into humans has been unsuccessful both for cell-seeded and acellular scaffolds. This can be ascribed to various factors, including the use of only non-diseased models that inaccurately describe the structural and functional modifications of diseased tissue. The paper addresses potential future strategies to overcome the limitations experienced in clinical applications so far. This includes the use of stem cells of various origins (mesenchymal stem cells, hematopoietic stem/progenitor cells, urine-derived stem cells, and progenitor cells of the urothelium) as well as the need for a deeper understanding of signaling pathways and directing tissue ingrowth and differentiation through the concept of dynamic reciprocity. The development of smart scaffolds that release trophic factors in a set and timely manner will probably improve regeneration. Modulation of innate immune response as a major contributor to tissue regeneration outcome is also addressed. It is unlikely that only one of these strategies alone will lead to clinically applicable tissue engineering strategies in pediatric urology. In the meanwhile, the fundamental new insights into regenerative processes already obtained in the attempts of tissue engineering of the lower urogenital tract remain our greatest gain.

Acellular Mouse Kidney ECM can be Used as a Three-Dimensional Substrate to Test the Differentiation Potential of Embryonic Stem Cell Derived Renal Progenitors

The development of strategies for tissue regeneration and bio-artificial organ development is based on our understanding of embryogenesis. Differentiation protocols attempt to recapitulate the signaling modalities of gastrulation and organogenesis, coupled with cell selection regimens to isolate the cells of choice. This strategy is impeded by the lack of optimal in vitro culture systems since traditional culture systems do not allow for the three-dimensional interaction between cells and the extracellular matrix. While artificial three-dimensional scaffolds are available, using the natural extracellular matrix scaffold is advantageous because it has a distinct architecture that is difficult to replicate. The adult extracellular matrix is predicted to mediate signaling related to tissue repair not embryogenesis but existing similarities between the two argues that the extracellular matrix will influence the differentiation of stem and progenitor cells. Previous studies using undifferentiated embryonic stem cells grown directly on acellular kidney ECM demonstrated that the acellular kidney supported cell growth but limited differentiation occurred. Using mouse kidney extracellular matrix and mouse embryonic stem cells we report that the extracellular matrix can support the development of kidney structures if the stem cells are first differentiated to kidney progenitor cells before being applied to the acellular organ.

Urinary Tissue Engineering: Challenges and Opportunities

INTRODUCTION

In this review, we discuss major advancements and common challenges in constructing and regenerating a neo-urinary conduit (NUC). First, we focus on the need for regenerating the urothelium, the hallmark the urine barrier, unique to urinary tissues. Second, we focus on clinically feasible scaffolds based on decellularized matrices and molded collagen that are currently of great research interest.

AIM

To discuss the major advancements in constructing a tissue-engineered NUC (TE-NUC) and the challenges involved in their successful clinical translation.

METHODS

A comprehensive search of peer-reviewed literature from PubMed and Google Scholar on subjects related to urothelium regeneration, decellularized tissue matrices, and collagen scaffolds was conducted.

MAIN OUTCOME MEASURE

We evaluated the main biological and mechanical functions of urinary tissues, the need for TE implants to create a urinary diversion, the reasons for their failures in clinical settings, and the applications of decellularized tissue matrices and collagen-based molded scaffolds in their regeneration.

RESULTS

It is necessary to create a urine barrier that prevents urine leakage into the stroma that can cause failure of the graft. Despite the regeneration potential of the urothelium, the limited supply of healthy urothelial cells in patients with bladder cancer remains a major challenge. In this context, alternative strategies, such as transdifferentiation of cells into urothelium or engineered scaffolds based on decellularized tissues and molded collagen with robust urine barrier properties, are active areas of research.

CONCLUSION

There is an immediate need for developing a functional TE-NUC that can improve the quality of life of patients with bladder cancer. It is possible to achieve a TE-NUC by bioengineering an implant that has appropriate biological and mechanical properties to store and transport urine. We anticipate that future advancements in urothelium regeneration and material design will lead us closer to successful neo-urinary tissue constructs. Singh A, Bivalacqua TJ, Sopko N. Urinary Tissue Engineering: Challenges and Opportunities. Sex Med Rev 2018;6:35-44.

Tissue engineering for urinary tract reconstruction and repair: Progress and prospect in China

Several urinary tract pathologic conditions, such as strictures, cancer, and obliterations, require reconstructive plastic surgery. Reconstruction of the urinary tract is an intractable task for urologists due to insufficient autologous tissue. Limitations of autologous tissue application prompted urologists to investigate ideal substitutes. Tissue engineering is a new direction in these cases. Advances in tissue engineering over the last 2 decades may offer alternative approaches for the urinary tract reconstruction. The main components of tissue engineering include biomaterials and cells. Biomaterials can be used with or without cultured cells. This paper focuses on cell sources, biomaterials, and existing methods of tissue engineering for urinary tract reconstruction in China. The paper also details challenges and perspectives involved in urinary tract reconstruction.

The effect of a cyclic uniaxial strain on urinary bladder cells

Purpose

Pre-conditioning of a cell seeded construct may improve the functional outcome of a tissue engineered construct for augmentation cystoplasty. The precise effects of mechanical stimulation on urinary bladder cells in vitro are not clear. In this study we investigate the effect of a cyclic uniaxial strain culture on urinary bladder cells which were seeded on a type I collagen scaffold.

Methods

Isolated porcine smooth muscle cells or urothelial cells were seeded on a type I collagen scaffolds and cultured under static and dynamic conditions. A uniform cyclic uniaxial strain was applied to the seeded scaffold using a Bose Electroforce Bio-Dynamic bioreactor. Cell proliferation rate and phenotype were investigated, including SEM analysis, RT-PCR and immunohistochemistry for α-Smooth muscle actin, calponin-1, desmin and RCK103 expression to determine the effects of mechanical stimulation on both cell types.

Results

Dynamic stimulation of smooth muscle cell seeded constructs resulted in cell alignment and enhanced proliferation rate. Additionally, expression of α-Smooth muscle actin and calponin-1 was increased suggesting differentiation of smooth muscle cells to a more mature phenotype.

Conclusions

Mechanical stimuli did not enhance the proliferation and differentiation of urothelial cells. Mechanical stimulation, i.e., preconditioning may improve the functional in vivo outcome of smooth muscle cell seeded constructs for flexible organs such as the bladder.

Electronic supplementary material

The online version of this article (doi:10.1007/s00345-017-2013-9) contains supplementary material, which is available to authorized users.

Intraosseous Injection of Simvastatin in Poloxamer 407 Hydrogel Improves Pedicle-Screw Fixation in Ovariectomized Minipigs

BACKGROUND

Osteoporosis leads to poor osseointegration and reduces implant stability. Statins have been found to stimulate bone formation, but the bioavailability from oral administration is low. Local application may be more effective at augmenting bone formation and enhancing implant stability. This study was performed to evaluate the efficacy of an intraosseous injection of simvastatin in thermosensitive poloxamer 407 hydrogel to enhance pedicle-screw fixation in calcium-restricted ovariectomized minipigs.

METHODS

Nine mature female Guangxi Bama minipigs underwent bilateral ovariectomy and were fed a calcium-restricted diet for 18 months. Simvastatin (0, 0.5, or 1 mg) in thermosensitive poloxamer 407 hydrogel was injected into the lumbar vertebrae (L4-L6), and titanium alloy pedicle screws were implanted. Bone mineral density (BMD) measurements of the lumbar vertebrae were determined by dual x-ray absorptiometry (DXA) before and 3 months after treatment. The lumbar vertebrae were harvested and analyzed with use of microcomputed tomography, biomechanical pull-out testing, histological analysis, and Western blot analysis for bone morphogenetic protein (BMP)-2 and vascular endothelial growth factor (VEGF) expression.

RESULTS

Evaluation over a 3-month study period demonstrated that the BMD of the vertebrae injected with 0.5 and 1.0 mg of simvastatin had increased by 31.25% and 31.09%, respectively, compared with vehicle-only injection (p ≤ 0.00014 for both) and increased by 32.12% and 28.16%, respectively, compared with the pre-treatment levels (p < 0.0001 for both). A single injection of simvastatin in poloxamer 407 increased trabecular volume fraction, thickness, and number and decreased trabecular separation (p ≤ 0.002). The bone formation and mineral apposition rates significantly increased (p ≤ 0.023). The percentage of osseointegration in the simvastatin 0.5 and 1-mg groups was 46.54% and 42.63% greater, respectively, than that in the vehicle-only group (p ≤ 0.006), and the maximum pull-out strength was 45.75% and 51.53% greater, respectively, than in the vehicle-only group (p ≤ 0.0005). BMP-2 and VEGF expressions were higher than for the vehicle-only injection.

CONCLUSIONS

A single intraosseous injection of simvastatin in thermosensitive poloxamer 407 hydrogel stimulated bone formation, increased BMD, improved bone microstructure, promoted osseointegration, and significantly enhanced the stability of pedicle screws in calcium-restricted ovariectomized minipigs.

CLINICAL RELEVANCE

These results provide rationale for evaluating intraosseous injection of simvastatin in poloxamer 407 to enhance implant fixation in patients with osteoporosis.

Isolation, expansion and characterization of porcine urinary bladder smooth muscle cells for tissue engineering

Background

A key requirements for therapy utilizing the tissue engineering methodologies is use of techniques which have the capability to yield a high number of cells, from small tissue biopsy in a relatively short time. Up to date there was no optimal methods of isolation and expansion of urinary bladder smooth muscle cells (UB-SMCs). The aim of this study was to compare isolation and expansion techniques of UB-SMCs to select the most repeatable and efficient one.

Method

Five protocols of porcine UB- SMCs isolation including enzymatic and explant techniques and three expansion techniques were compared. Isolation effectiveness was evaluated using trypan blue assay. Cell phenotype was confirmed by immunofluorescence staining. Proliferation rate was analyzed using MTT and X- Celligence system. Cellular senescence was assessed measuring β-galactosidase activity.

Results

Enzymatic methods using collagenase with dispase (method I) or collagenase only (method III) allowed to isolate much larger number of cells than the methods using trypsin with collagenase (method II) and collagenase after digestion with trypsin (method IV). The success rate of establishment of primary culture was the highest when the isolated cells were cultured in the Smooth muscle Growth Medium-2 (SmGM-2). Expression of the smooth muscle markers- alpha smooth muscle actin and smoothelin was the highest for cells isolated by enzymatic method I and cultured in SmGM-2. There was no significant signs of cell senescence until the 8th passage.

Conclusion

The most efficient method of establishment of porcine UB-SMCs culture is enzymatic digestion of urinary bladder tissue with collagenase and dispase and culture of isolated cells in SmGM-2. This method was up to 10 times more efficient than other methods used for isolation and culture of UB-SMCs. This is an easy and consistent method for obtaining high numbers of urinary bladder smooth muscle cells.

Silk Fibroin Scaffolds for Urologic Tissue Engineering

Urologic tissue engineering efforts have been largely focused on bladder and urethral defect repair. The current surgical gold standard for treatment of poorly compliant pathological bladders and severe urethral stricture disease is enterocystoplasty and onlay urethroplasty with autologous tissue, respectively. The complications associated with autologous tissue use and harvesting have led to efforts to develop tissue-engineered alternatives. Natural and synthetic materials have been used with varying degrees of success, but none has proved consistently reliable for urologic tissue defect repair in humans. Silk fibroin (SF) scaffolds have been tested in bladder and urethral repair because of their favorable biomechanical properties including structural strength, elasticity, biodegradability, and biocompatibility. SF scaffolds have been used in multiple animal models and have demonstrated robust regeneration of smooth muscle and urothelium. The pre-clinical data involving SF scaffolds in urologic defect repair are encouraging and suggest that they hold potential for future clinical use.

Acellularization-Induced Changes in Tensile Properties Are Organ Specific - An In-Vitro Mechanical and Structural Analysis of Porcine Soft Tissues

Introduction

Though xenogeneic acellular scaffolds are frequently used for surgical reconstruction, knowledge of their mechanical properties is lacking. This study compared the mechanical, histological and ultrastructural properties of various native and acellular specimens.

Materials and Methods

Porcine esophagi, ureters and skin were tested mechanically in a native or acellular condition, focusing on the elastic modulus, ultimate tensile stress and maximum strain. The testing protocol for soft tissues was standardized, including the adaption of the tissue’s water content and partial plastination to minimize material slippage as well as templates for normed sample dimensions and precise cross-section measurements. The native and acellular tissues were compared at the microscopic and ultrastructural level with a focus on type I collagens.

Results

Increased elastic modulus and ultimate tensile stress values were quantified in acellular esophagi and ureters compared to the native condition. In contrast, these values were strongly decreased in the skin after acellularization. Acellularization-related decreases in maximum strain were found in all tissues. Type I collagens were well-preserved in these samples; however, clotting and a loss of cross-linking type I collagens was observed ultrastructurally. Elastins and fibronectins were preserved in the esophagi and ureters. A loss of the epidermal layer and decreased fibronectin content was present in the skin.

Discussion

Acellularization induces changes in the tensile properties of soft tissues. Some of these changes appear to be organ specific. Loss of cross-linking type I collagen may indicate increased mechanical strength due to decreasing transverse forces acting upon the scaffolds, whereas fibronectin loss may be related to decreased load-bearing capacity. Potentially, the alterations in tissue mechanics are linked to organ function and to the interplay of cells and the extracellular matrix, which is different in hollow organs when compared to skin.

Bladder Acellular Matrix Grafts Seeded with Adipose-Derived Stem Cells and Incubated Intraperitoneally Promote the Regeneration of Bladder Smooth Muscle and Nerve in a Rat Model of Bladder Augmentation

The objective of this study was to investigate the feasibility of bladder acellular matrix grafts (BAMGs) seeded with adipose-derived stem cells (ASCs) followed by intraperitoneal incubation for bladder reconstruction in a rat model of bladder augmentation, and to explore the underlying mechanism. Autologous CM-DiI-labeled ASC-seeded (experimental group) and unseeded (control group) BAMGs were incubated in the peritoneum of male rats for 2 weeks and then harvested for bladder augmentation. Histological analysis of the incubated BAMGs revealed numerous cells growing in homogeneous collagen bundles in both groups. In the control BAMGs, these cells were mesenchyme derived, while in the ASC-seeded BAMGs, myofibroblasts and mesothelial cells were found inside and on the surface of the scaffold, respectively. Immunofluorescence analysis demonstrated that some of the myofibroblasts were transdifferentiated from the ASCs after 2 weeks of intraperitoneal incubation. The greater bladder capacity was found in the experimental group than the control group both 4 and 14 weeks postoperatively. Histological analysis revealed that the entire urothelium regenerated well both in the experimental group and the control group without significant difference 4 weeks and 14 weeks postoperatively. From the quantitative data of immunohistochemical and immunofluorescence staining, the smooth muscle cells (SMCs) regenerated significantly better in the experimental group than the control group both 4 weeks and 14 weeks postoperatively. Also significantly more nerve cells were found in the experimental group 14 weeks postoperatively. At 4 weeks postoperatively, the immunofluorescence double staining revealed that some SMCs in the BAMG were transdifferentiated from the implanted ASCs, but no CM-DiI labeling of ASCs was detected 14 weeks postoperatively. Taken together, our results demonstrate that ASC-seeded and peritoneally incubated BAMGs promote not only the morphological regeneration of the bladder smooth muscle and nerve, but also the bladder capacity, which indicates their potential for bladder regeneration.

Co-delivery of VEGF and bFGF via a PLGA nanoparticle-modified BAM for effective contracture inhibition of regenerated bladder tissue in rabbits

Graft contracture is a common problem associated with the regeneration processes of tissue-engineered bladders. Currently, most strategies used for incorporating bioactive molecules into biomaterial designs do not work during all phases of tissue regeneration. In this study, we used a growth factor-PLGA nanoparticle thermo-sensitive gel system (i.e., BAM with incorporated VEGF and bFGF-loaded PLGA nanoparticles and mixed with a hydrophilic gel) to promote bladder tissue regeneration in a rabbit model. At 4 and 12 weeks after surgery, contracture rate assessment and histological examination were conducted to evaluate bladder tissue regeneration. The results indicated that the functional composite scaffold continuously and effectively released VEGF and bFGF and promoted bladder reconstruction with a significant decrease in graft contracture. In addition, the number and arrangement of regenerated urothelial cells and smooth muscle cells as well as microvascular density and maturity were improved in the VEGF/bFGF nanoparticle group compared with the single factor VEGF or bFGF nanoparticle group and BAM alone. The nanoparticle thermo-sensitive gel system, which exhibited favourable performance, may effectively inhibit graft contracture and promote bladder tissue regeneration in rabbits.

Organ-specific matrix self-assembled by mesenchymal cells improves the normal urothelial differentiation in vitro

PURPOSE

Enterocystoplasty is the gold standard to perform bladder reconstruction. Since this technique has a high morbidity rate, several matrix scaffolds have been proposed to support the urothelial maturation. Unfortunately, epithelial cells failed to fully integrate the cell-matrix interactions and therefore appropriate signalling pathways of normal differentiation. Based on these observations, we proposed to culture bladder urothelial cells (BUC) onto a matrix self-assembled by bladder mesenchymal cells (BMC), to form a vesical model (VM).

METHODS

Different serum proportions were assessed to obtain a manipulable matrix deposited by BMC. The BUC were then seeded onto the BMC's matrix to evolve in a three-dimensional culture. Haematoxylin-eosin staining, immunolabeling, scanning electron microscopy, western blot and matrix metalloproteinases analysis were performed for the VM characterization.

RESULTS

We were able to obtain an original matrix made of collagen-I and presenting specific organization. Matrix remodelling was observed and led to a cellular compartmentalization. The reconstructed urothelium developed in a pseudostratified arrangement, displaying an adequate cellular polarity and apical membrane remodelling of superficial cells. Like native bladder, cytokeratin 14 immunolabeling was not observed in our VM, which indicate the conformity of the development sequence taken by BUC under the influence of the BMC's matrix.

CONCLUSION

Thus, it was possible to elaborate a VM without the use of exogenous matrices. The particular characteristics of the BMC's matrix permitted the development of an urothelium that shared the phenotype of native tissue. The autologous character of our VM, and its appropriate urothelial maturation, could potentially promote a better integration after grafting.

Bladder reconstruction: The past, present and future

Ileal conduit urinary diversion is the gold standard treatment for urinary tract reconstruction following cystectomy. This procedure uses gastrointestinal segments for bladder augmentation, a technique that is often associated with significant complications. The substantial progression in the fields of tissue engineering and regenerative medicine over the previous two decades has resulted in the development of techniques that may lead to the construction of functional de novo urinary bladder substitutes. The present review identifies and discusses the complications associated with current treatment options post-cystectomy. The current techniques, achievements and perspectives of the use of biomaterials and stem cells in the field of urinary bladder reconstruction are also reviewed.